1. Field of the Invention
The present invention relates to liners for use with prosthetics and similar devices worn in close contact with a wearer's skin where dissipation of perspiration is a concern.
2. Description of Related Art
A common problem in placing any material with low or no air permeability ("breathability") in contact with a wearer's skin is that perspiration cannot evaporate and tends to build-up between the skin and the non-breathable material. With only passing use, this condition leads to an uncomfortable damp or clammy feeling. In more extreme circumstances, such as with the prolonged use of a prosthetic device covering a limb, the accumulation of moisture fully hydrates the skin, which in its softened, wet condition leads to skin irritation, maceration, and rapid bacteria growth.
The problem of moisture build-up with prosthetic use is a particularly serious one. Generally prosthetic devices such as artificial limbs must be constructed from durable material to withstands the vigors of use. Materials such as metal or high impact plastic provide the necessary degree of durability, but offer very poor breathability.
The problem of moisture build-up in the interface with prosthetic devices is particularly dangerous for diabetic patients, and especially those experiencing Peripheral Vascular Disease (PVD). PVD is a major cause of amputation in the United States and a patient typically experiences amputation of a lower limb within 20 years of its onset. This is because impaired circulation affects nerve endings, so sensation is decreased, and minor bruising, rubbing or skin irritation can occur without the patient experiencing any discomfort. A minor break in the skin can quickly lead to ulceration, possible gangrene and eventual amputation.
Dry skin normally equates to healthy skin and this is particularly true for certain high risk groups, such as a diabetic with PVD. Use of a non-breathing attachment to a prosthetic device, such as neoprene or silicone, which is fitted as a second skin having little or no air gap, necessitates frequent changes of a separate absorbent layer, or else moisture vapor generated by the pores of the wearer's skin transforms to liquid and hydrates and softens the skin. When totally hydrated, "immersion skin" develops and any pressure or movement caused by loose fitting prosthesis or liner on the softened skin results in a blister type formation, and large areas of skin debraiding.
To address the problem of moisture build-up, traditionally the wearer of a prosthetic device has employed a thick sock of wool or similar material between his or her skin and the prosthetic. This has accomplished a number of important functions, including providing a wick to remove perspiration from the skin, improving the fit between the wearer and the device, and cushioning the wearer from shock during usage. Unfortunately, the sock performed none of these functions particularly well. As a wick, a conventional sock device tends to be good at initial moisture removal, but will eventually become saturated with moisture requiring repeated changing. Additionally, with materials such as wool, odor control with the wet material was another unpleasant problem. Due to constraints of conventional materials, the sock-type device was even poorer in performance in providing fit and comfort to the wearer. As a result, conventional prosthetics did not fit well and offered meager shock absorption.
More recent advances have provided vast improvements in the fit and shock absorption of prosthetic devices. The inclusion of tight fitting interfaces of neoprene or silicone rubber and similar materials assure that devices can be kept snugly in place during use and that the wearer will be effectively cushioned from shock. Regrettably, these materials only worsen the problem of moisture retention, with the tighter elastomeric fit offering reduced opportunity for moisture dissipation and the typical cushioning layer being poor at removing moisture away from the wearer's skin.
In response to some of these concerns, it was proposed in UK Patent Application GB 2,213,380, published Aug. 16, 1989, to form a limb cover from a waterproof yet breathable microporous expanded polytetrafluoroethylene (PTFE) membrane which will permit the passage of moisture through it into an absorbent layer such as a sock. The absorbent sock serves to absorb perspiration and allows it to evaporate from the exposed surfaces of the sock; the membrane serves to prevent perspiration from passing back through to the wearer's skin. In order to get the membrane to fit on the wearer's limb, it is taught that a single membrane should be cold formed into a cup-shaped area suitable for insertion of the limb. The excess remainder of the membrane is then folded and wrapped around the sides of the limb.
While the above device may work well for its intended purposes, it simply fails to address many of the concerns presented by improved prosthetic devices. First, the method of forming and wearing the PTFE membrane is simply inadequate for comfortable use of improved cushioning devices. For example, when inserted into a tight fitting silicone sleeve regularly worn between the wearer and the prosthesis, the bunching of the PTFE material around the side of the limb can lead to chafing and masceration.
Second, the use of non-absorbent devices like silicone sleeves simply cannot provide the absorbance sought with absorbent wool or acrylic socks. As a result, either the silicone sleeve must be worn over the absorbent sock--diminishing fit and feel, or the material must be worn without an absorbent layer--removing the intended mechanism for dissipating the moisture.
Third, the British reference does not address the concern that expanded PTFE membranes can become contaminated with oils from the body which can result in loss of their water repellency. This may be of limited concern when worn in contact with an absorbent layer which can wick moisture away from the membrane, but is fatal to the operation of the device if the membrane is employed with no absorbent layer.
A different use of a lining material is disclosed in U.S. Pat. No. 5,016,622 issued May 21, 1991, to Jean Norvell. This device comprises a tube or wrap of expanded PTFE used as a liner for orthopedic casts. The tube or wrap is covered with a layer of padding (e.g. cotton or polyester), from which evaporation can occur, which is in turn coated with the immobilizing layer of the cast. Although this device works quite well for its intended purposes, the teaching of this patent again relies upon a separate absorbent layer to dissipate moisture away from the wearer as well as a rigid casting material, cushioned by padding, open at the distal and proximal ends of the cast. This construction guarantees a small air gap will remain between the skin and the casting material to allow the evaporation of moisture.
By contrast, a prosthetic device is custom fitted to a wearer as a "second skin" through a process of negative and positive molds. As such, the prosthesis represents the exact contours of the wearer's limb, with virtually no ease allowed whatsoever. In fact, in some prostheses, a partial vacuum is deliberately induced within the interface to the limb to ensure increased fit in the device and the total exclusion of any air gap. In this respect U.S. Pat. No. 5,016,622 offers no instruction of how to improve the interface between a prosthetic device and its wearer.
In other fields besides prosthetics, similar concerns have arisen. For example, it is common practice in many sports such as football and ice hockey to employ extensive pads and braces to protect against injury. The more extensive of these pads generally comprise hard, impervious shells with a layer of foam or other resilient material coated within. Not surprisingly, in the course of athletic contests a tremendous moisture build-up can occur within these pads which can lead to discomfort and skin irritation. While various absorbent materials such as cotton or polymer fabrics are regularly worn under some of these pads to absorb excess moisture, this provides only limited relief and does not serve to isolate the wearer's skin adequately from the perils of moisture build-up.
Other areas of concern where moisture-build up can occur beneath a non-breathable material include the use of orthotic body supports, cam walkers and other orthotics, orthosis systems, and braces, as well as immobilizing braces and devices used to treat cumulative trauma disorders. Additionally, moisture accumulation is likewise a problem with other pads and safety garments (e.g. flak jackets) which provide limited breathability while worn in intimate contact with the skin.
Accordingly, it is a primary purpose of the present invention to provide a liner for a substantially non-breathable shell worn against a wearer's skin which effectively isolates moisture from the wearer skin.
It is another purpose of the present invention to provide such a liner which provides a smooth fit between the wearer and the shell so as to avoid problems of chafing and other skin irritation.
It is still another purpose of the present invention to provide such a liner which can be safely worn in direct contact with a wearer's skin, even during periods of excess perspiration, without compromising its effectiveness.
It is an additional purpose of the present invention to provide a liner which can effectively isolate a wearer's skin from moisture even when worn without a separate absorbent layer.
It is yet another purpose of the present invention to provide methods for constructing and employing such a liner which will provide the above benefits.
These and other purposes of the present invention will become evident from review of the following specification.